Answer:
Savvy direct mail marketers know that you need to burrow deep into prospect lists to hit gold. A random selection of names from a general list will only allow you to scrape the surface, and you may never determine the real value of the list. Here are some selects that have yielded big dividends:

Last- three-month buyers - previous behavior is one of the best indications of future behavior. Cherry-pick the most recent buyers, as they are most likely to be in a purchasing frame of mind.

Gender select - depending on your offer, try males first, then females. Then ask your broker for names with "no gender specified." Since your competition may not be mailing to these names, your piece is likely to receive more attention -- and a response boost is nearly ensured!

Past purchase amount - if you have a $59 offer, you probably won't do well addressing buyers who have no history of paying more than $20 in the past. In this case, start off with a $50+ select.

High-frequency buyers - you'll always do better with folks who have purchased numerous times from other vendors versus single buyers. Zero in on 2x, 3x, even 5x buyers for the best results.